1. Field of the Invention
This invention relates to improved gate valve apparatus of the type commonly used in association with chemical processes or the like which may experience a hazard condition or upset requiring rapid valve actuation to prevent a catastrophic failure. More particularly, the invention relates to a gate valve apparatus provided with an actuator which generates a gas discharge at a subsonic flow rate in order to rapidly and smoothly shift a valve member for actuation of the gate valve apparatus. Structure is also provided in association with the valve member to control the rate of deceleration of the gate valve.
2. Description of the Prior Art
Isolation-type gate valves have long been provided with chemical reactor apparatus for the purpose of allowing rapid shutdown of the reactor in the event of generation of hazardous conditions. In general, such gate valves include a valve body which presents a passageway therethrough, with a shiftable, apertured valve member within the body and normally located in a valve open position allowing flow through the valve. The valve member is shiftable to a flow-blocking valve closed position when a hazardous condition is sensed.
The actuators associated with prior gate valves have included mechanical linkages operated by motors or solenoids for example. However, in some instances prior actuators are unable to actuate a gate valve with sufficient rapidity to prevent flame propagation, actual passage of a flame through the gate, explosion, or some other significant failure. Additionally, in some contexts, it is desirable to avoid generation of electrical sparks which may occur with motor driven gate valve assemblies.
U.S. Pat. No. 3,358,961 of Dec. 19, 1967, represents another type of gate valve for releasing pressure in a fluid flow system. In this instance, a sliding valve is operated by an explosive charge producing a supersonic shock wave for extreme accelerated shifting of the valve body from a normally closed position to a fully opened location. The shutter-type valve is useful only for relatively small orifice applications involving a similarly limited size valve assembly. The valve body and associated shutter plate and piston assembly must be small enough that no damage is caused to the valve components by shock waves generated upon actuation of the explosive device, or as a result of inertia upon impact of the shutter plate with the housing assembly during valve closing.
Accordingly, there is a need in the art for an improved isolation gate valve assembly, and a corresponding method of gate valve operation, which avoids the problems of prior valve actuators.